Process of preparing multiple copies from a xeroprinting master

ABSTRACT

THIS APPLICATION RELATES TO A METHOD OF PREPARING A NOVEL XEROPRINTING MASTER UTILIZING ELECTROPHORETIC PRINCIPLES. UPON INTRODUCING AN INSULATING MATERIAL INTO A PHOTOELECTROPHORETIC IMAGING SUSPENSION IT HAS BEEN DETERMINED THAT THE AREAS FROM WHICH THE PHOTOSENSITIVE PARTICLES MIGRATE BECOME INSULATING AND CAPABLE OF SUPPORTING AN ELECTROSTATIC CHARGE IN AN IMAGEWISE PATTERN.

, L.- M. CARREIRA ,EROCESS 0F PREPARING MULTIPLE COPIES FROM A XEROPRINTING MASTER Flled Jan. 6, 1967 April H,

2 Sheets-Sheet 2 All, 53 1+ z INVENTOR.

LEyARD M.CAR IRA BY 1 ATTORNEYS United States Patent 3,574,614 PROCESS OF PREPARING MULTIPLE COPIES FROM A XEROPRINTING MASTER Leonard M. Carreira, Webster, N.Y., assignor to Xerox Corporation, Rochester, N.Y. Filed Jan. 6, 1967, Ser. No. 607,747 Int. Cl. G03g 13/16, 13/22,- B41m 1/06 U.S. Cl. 96-1.4 2 Claims ABSTRACT OF THE DISCLOSURE This application relates to a method of preparing a novel xeroprinting master utilizing electrophoretic principles. Upon introducing an insulating material into a photoelectrophoretic imaging suspension it has been determined that the areas from which the photosensitive particles migrate become insulating and capable of supporting an electrostatic charge in an imagewise pattern.

This invention relates to a printing system and, more specifically, to a xeroprinting duplicating system.

In the art of duplicating, various techniques have been developed for preparing masters for subsequent use in printing processes. One of the more classical known of these techniques is the production of carbon copies in a typewriter. Aside from the limited number of legible copies that may be produced, this technique is burdened with several inherent deficiencies. For example, the texture of the paper used in making copies must generally be extremely light weight in order to transmit pressure for at least two or three copies. In addition, in the event that more than a couple of copies are desired, it is necessary to exert extremely high pressures on the type characters resulting in the embossment of the original. Moreover, the readability of the carbon copies drops off with each additional reproduction.

In order to overcome the many difficulties inherent in the production of duplicates with carbon paper, a number of duplicating techniques utilizing variously formed printing masters have been developed. For example, lithographic or offset printing is a Well known and established printing process. In general, lithography is a method of printing from a fiat plate which depends upon different properties of the image and non-image areas for printability. In conventional lithography, the non-image area is hydrophilic or water receptive while the image area is hydrophobic or water repellant. The printing master is first contacted with a fountain solution which wets all portions of the surface not covered by the hydrophobic image. An oil based printing ink is then applied to achieve the desired selective inking in the image areas. Usually, the ink image on the master is then transferred to an offset roller from where the actual printing takes place. Although simplifying production of masters, there are basic disadvantages which make this method of printing undesirable. Ordinarily, it is required that a conversion solution be used in order to impart to the initially hydrophobic background or non-image areas the necessary hydrophilic properties. Furthermore, it is difficult to maintain the proper water to ink balance required during the printing phase of the process. In addition, the introduction of an intermediate step into the printing process, that of transferring the image from the printing plate to an offset roller, increases the possibility of impairing the resolution of the printing image.

Letterpress printing is considered the oldest and most commonly used method of printing. Ink is applied to a raised surface and transferred directly to a support substrate through pressure. The areas to be printed are raised above the nonprinting areas and the ink rollers touch 3,574,614 Patented Apr. 13, 1971 only the top surface of the raised areas. The surrounding, non-printing areas are lower and do not receive ink. While popular, letterpress printing is not without its disadvantages. Considerable time is consumed in the makeready of the printing plate, with the procedures generally utilized requiring strict control measures to produce the desired results.

Still a third type of printing known as gravure printing uses a sunken or depressed surface for transferring the image. A plate or cylinder with the image etched below its surface rotates in a bath of ink. The excess ink is wiped off the surface by a doctor blade. The ink remaining in thousands of recessed cells forms the image by direct transfer to the paper as it passes between the plate and impression cylinders. Although quite effective, this system is also limited by requiring strictly controlled plate make-ready procedures.

It is, therefore, an object of this invention to provide a printing system which will overcome the above noted disadvantages.

It is a further object of this invention to provide a process of using a novel printing plate.

Another object of this invention is to provide a novel method for the preparation of a printing master.

Still a further object of this invention is to provide a novel printing systemwhich eliminates the expensive and time consuming make-ready procedures heretofore generally accepted as necessary.

Yet, still a further object of this invention is to provide a novel process for the preparation of a printing master capable of producing direct positive prints.

The foregoing objects and other are accomplished in accordance with this invention, generally speaking, by providing a suspension of photoelectrophoretic imaging particles in an insulating carrier liquid. This suspension is placed between a pair of electrodes and subjected to a potential difference while simultaneously being exposed to a reproducible image. Generally speaking, the imaging suspension is placed on a transparent electrically conductive imaging plate or first electrode in the form of a. thin film, and exposure is made through the transparent plate while in contact with a second electrode which is placed or rolled over the top of the imaging suspension. The particles present in the suspension migrate in response to electromagnetic radiation to form a visible image pattern at one or both of the electrodes, the images being opposite in sense to one another. An insulating composition is then applied to the imaged film on the surface of the first transparent conductive electrode and the surface subsequently charged to a predetermined potential in the presence of electromagnetic radiation. Electrostatic charge is retained on those areas of the film void of the photosensitive imaging particles referred to herein as the nonimage areas. Thus, in essence there has been produced a Xeroprinting master which may be utilized in a true mass production printing process. The resulting latent image thereby formed may be developed with pigmented resinous toner particles or a liquid developer with the developed image being subsequently transferred in an imagewise pattern to the surface of a copy sheet. The charging, developing and transferring steps may be repeated until the desired number of copies of the original image are produced.

As a result of the process of the present invention, it is possible to produce direct positive copies of original negative transparencies, or if desired, to produce direct negative copies from positive transparencies. When the negative copy is reproduced it may be desirable to introduce a development electrode into the system such as disclosed in U.S. Pats. 2,573,881 and 3,147,147 in order to enhance the solid area coverage of the image. The

system of the present invention is particularly useful in the production of monochromatic line copy images by using single color particles in the suspension or a number of differently colored particles in the suspension which will respond during exposure to a mixture of light. Furthermore, when desirable, the photoelectrophoretic image formed on the surface of the imaging electrode may be transferred by any suitable technique, such as by electrostatic means, as more fully described in US. patent application Ser. No. 542,050, filed Apr. 12, 1966 and having a common assignee, or by an adhesive transfer technique, to the surface of a conductive substrate which in turn may be treated with the insulating material as discused above to produce the desired efiect and the resulting plate used as the xeroprinting master. This procedure eliminates the necessity of printing from the imaging electrode thereby lending flexibility to the printing system.

Alternatively, the above disclosed insulating composition or binder may be intimately blended with the dis persion of the photoelectrophoretic imaging particles prior to application to the surface of the imaging electrode. This approach eliminates the necessity of applying the insulating material subsequent to formation of the photoelectrophoretic image.

It has been determined in the course of the present invention that upon introducing an insulating material into a photoelectrophoretic imaging suspension or by applying the dielectric insulating material subsequent to the electrophoretic image formation step that the areas from which the photosensitive particles have migrated upon response to the exposure step become insulating in nature and capable of supporting an electrostatic charge. There is thereby produced an imaging surface substan tially photoconductive with an insulating image formed on or in its surface capable of supporting an electrostatic charge.

The invention is further illustrated in the accompanying drawings in which:

FIG. 1 is a side sectional view of an exemplary photoelectrophoretic imaging system of the present invention;

FIG. 2 represents a side sectional view of the imaging electrode of FIG. 1 undergoing insulating treatment;

FIG. 3 represents a diagrammatic view of the imaging electrode of FIG. 2 illustrating areas of photoconductivity and areas of insulation;

FIG. 4 represents a magnified cross section of the imaging electrode of FIG. 3 undergoing charge exposure;

FIG. 5 is a side sectional view illustrating exposure and the resulting effect on the charged surface of the imaging member of the present invention;

FIG. 6 illustrates the development of the latent image produced according to the exposure step illustrated in FIG. 5,;

FIG. 7 illustrates the xeroprinting transfer step of the present invention; and

FIG. 8 represents an illustration of a final print produced according to the process of the present invention.

FIG. 9 represents an exemplary printing apparatus utilizing the xeroprinting master prepared according to the process of the present invention.

Referring now to FIG. 1 there is seen a transparent conductive first electrode generally designated 1 which, in this instance, is made up of a layer of optically transparent glass 2 overcoated with a thin optically transparent layer 3 of tin oxide. Tin oxide coated glass of this nature is commercially available under the trade name NESA glass from the Pittsburgh Plate Glass Company. This electrode shall hereafter be referred to as the imaging or injecting electrode. Coated on the surface of the injecting electrode 1 is a thin layer 4 of finely-divided photosensitive pigment particles dispersed in an insulating liquid carrier. Above the liquid suspension 4 is passed a second or blocking electrode 7 which in this illustration is represented as a roller having a conductive central core 8 connected to a power source 11. The core in this instance is covered with a layer of blocking electrode material 9 which may, for example, be baryta paper. The pigment suspension is exposed by way of the projector mechanism generally designated 13 made up of a light source 14, a transparency 15, and a lens 16. For purposes of illustration a microfilm negative is used during the process. A potential is applied across the blocking and injecting electrodes upon the closure of switch 12. The blocking electrode 7, having a cylindrical configuration in the present illustration, is rolled across the top surface of the injecting electrode 1 supporting the electrophoretic suspension 4 with switch 12 closed during the period of image exposure. The light exposure causes the pigment particles suspended in the carrier and originally attracted to first electrode 1 to migrate in an imagewise manner through the liquid and adhere to the surface of the blocking electrode 7 thereby producing a positive pigment image 18 on the surface of the blocking electrode while leaving behind a negative pigment image 23 on the injecting electrode surface which is a duplicate of the original image 15 to which the injecting electrode 1 has been exposed. It should be noted at this point of the discussion that although the blocking electrode in the present illustration is represented as a cylinder it may also take the form of a planar electrode, as in the case of the illustrated injecting electrode, in which instance it would not be necessary for the injecting electrode to be optically transparent but instead the blocking electrode could be the optically transparent electrode and exposure made through it from above in a manner similar to the process described.

To the surface of the imaged injecting electrode 1 of FIG. 1 is applied an insulating composition 21, in the form of a spray, as illustrated by FIG. 2. The spray composition will generally consist of about 210'% binder with the balance being a substantially volatile carrier, such as toluene. Optimum results are obtained with about 4-7% binder. The insulating coating impregnates the film suspension 4 in both the image areas 23 and non-image areas 24 thereby producing in the substantially photoconductive dispersion coating a charge receptive image- Wise pattern at 24 which is opposite in sense to the image input. Although for purposes of this illustration, the application of the insulating binder is shown as being applied in the form of a mist or spray as a preferred embodiment, other suitable methods of introducing the insulating material may be utilized. For example, the liquid suspension 4 may have the insulating binder material incorporated therein, the remnants of which will remain behind .on the injecting electrode When the electrophoretic pigment particles are transferred by migration from the pigment dispersion during the exposure phase of the process. The binder concentration when included as a part of the imaging dispersion will amount to about 2r-25 by weight with a preferred optimum range being from about 46% by weight. In all instances the binder thickness Within the image formed will range from about 1 to about 20 with a preferred optimum thickness being 2 to 4 FIG. 3 represents a diagrammatic perspective view of the plate produced as a result of the procedure illustrated in FIG. 2. The electrophoretic image deposit 23 on the surface of the imaging electrode serves as the photosensitive element and the insulating binder image 2 4 as the charge receptive element. As a result of the inclusion in the system of the insulating component there has been produced on the surface of the injecting electrode, charge receptive areas forming an image pattern opposite in sense to the pigmented image. The pigmented images produced both on the injecting and blocking electrode surfaces are substantially fixed by the evaporation of the relatively volatile carrier liquid thereby presenting essentially non-tacky surfaces.

FIG. 4 represents the process step wherein the surface of the imaged injecting electrode is developed with an electrostatic charge, in the case of the present illustration the source being represented as a corona charging unit 32 powered by a power source 33. Upon exposure to a light source 35, as is illustrated in FIG. 5, the charge dissipates in those areas where the photosensitive particles are still present leaving an electrostatic latent image 37 on the surface of the electrode or plate 1 in the charge receptive areas 24. Charge is retained in an imagewise pattern supported by the insulating material which serves to insulate selective areas of the surface of the electrode from the underlying conductive NESA glass.

Following exposure of the charged plate as in FIG. 5, electroscopic powder developer 41 of FIG. 6 charged to a polarity in accordance with the result to be obtained is presented in any suitable manner, such as by cascade development as herein illustrated, or by powder cloud, magnetic brush or any other means known in the art, to the imaged plate or electrode 1. When it is desired that the developed image comprise an image developed corresponding to the areas of charge, it is generally preferred to pass in contact therewith a developer which is triboelectrically charged to a polarity opposite to the retained charge of the latent image whereby the developer is attracted and adheres to the charged areas of the insulative image pattern. However, when it is preferred that a developed image corresponding to the uncharged areas be reproduced, it is the general practice to employ developer charged to the same polarity as the image charge pattern. The developer will then be repelled by the charges of the latent image and will deposit on the non-charged areas of the plate with the charged areas remaining absent of developer. Continuing with FIG. 6 the developer material 41 has been permitted to fiow across the surface of the plate 1 making visible those portions of the image areas 37a contacted by developer 41. As herein illustrated, the cascade technique of development, as is more fully described in US. Pats. 2,618,551 and 2,618,552, utilizes a two element development mixture including finely-divided, electroscopic marking particles or toner and larger carrier beads. The carrier beads serve both to deagglomerate the fine toner particles for easier feeding and charge them by virtue of the relative positions of the toner and carrier material in the triboelectric series. The carrier beads with the toner particles clinging to them are cascaded across the surface of the plate from a hopper 43. The electrostatic field of the charge pattern on the drum attracts toner particles from the carrier beads thereby developing the image. The carrier beads along with any toner particles not used to develop the image, will be deposited into the receiver bin 45.

If it is desired to produce a negative image from a negative original or conversely a positive copy from a positive original transparency without using the reversal development procedure described above an alternate embodiment may be followed whereby the electrophoretic image formed on the surface of the blocking electrode may subsequently be transferred, by any suitable technique, such as by adhesive pick-off or electrostatically, to the surface of a secondary conductive substrate. A thin film of the insulating composition of the present invention may then be coated on the surface of the conductive image bearing substrate with a final effect being realized wherein there results a substantially photoconductive image on a conductive substrate with a substantial nonconductive image opposite in sense to the photoconductive image formed. This non-conductive image area may then be charged and developed as discussed above with the resulting toner image transferred to the final copy sheet and the process of charging and developing repeated to produce the desired number of copies.

FIG. 7 illustrates the transfer step of the xeroprinting process of the present invention wherein copy sheet 51, ordinary bond paper, is placed over the imaged surface of imaging electrode 1 and a charge 53 having a polarity opposite to that of the toner particles applied by way of charging unit 55 supplied by power source 56 to the back surface of the copy sheet 51. As a result of this step the loosely held toner particles 37a are attracted from the surface of imaging electrode 1 to the surface of the copy sheet 51 in response to the selective polarity of the charge applied. FIG. 8 is a diagrammatic view of the copy sheet 51 of FIG. 7 demonstrating the results of the transfer step wherein toner image 37a represents the final copy produced of the original image. The toner image may be fixed to the surface of the copy sheet by any suitable means such as vapor fusing, treatment of the developed image with a regulated amount of heat or by placing a lamination over the top surface of the transferred image.

FIG. 9 represents a simple continuous exemplary apparatus for carrying out the xeroprinting process of the present invention. In this apparatus, there is seen a rotary support 61 in the form of a drum which, in this instance, is made up of an aluminum base 62 carrying on its outer surface a thin optically transparent conductive layer 63 of chromium plated Mylar, the latter being polyethylene terephthalate available from E. I. du Pont de Nemours & Co., Inc. On the surface of the drum support 61 there is a fixed layer 64 of the electrophoretic imaging suspension of the present invention having formed therein a positive charge receptive image 65. The drum, when in operation, is generally rotated at a uniform velocity in the direction indicated by the arrow. After the drum surface passes the charging unit 67 and has been uniformly charged, it comes beneath an exposure mechanism 69 for exposing the charge surface to a source of electromagnetic radiation. Subsequent to charging and exposure, sections of the drum surface move past the developing unit generally designated 71. This unit is of the cascade type, as discussed above, which includes a powder container or cover 72 with a trough at the bottom containing a supply of developing material 73. The developing material is picked up from the bottom of the container and dumped or cascaded over the drum surface by a number of buckets 74 on an endless driven belt 75. The electrostatic field of the charge pattern developed on the charge receptive areas of the support drum attracts toner particles from the developer composition thereby developing the image. That portion of the developer which does not develop the image falls back into the bottom of container 72. Positioned next and adjacent to the developing station is the image transfer station generally designated 81 which includes a suitable sheet feeding mechanism 82 adapted to feed, in the case of the present illustration, sheets of paper successively to the drum in coordination with the presentation of the developed image 65a on the drum at the transfer station. The sheet feeding mechanism 82 introduces a transfer or copy sheet 87 between feed rollers 83 and the sheet is brought into contact with the rotating drum at the correct time and position to register with the developed image. The transfer of the toner powder image 65a on the drum surface to the copy material 87 is effected by means of a corona transfer device 84 which is located at or immediately after the point of contact between the transfer material and the rotating drum. The corona transfer device 84 is substantially similar to the corona discharge device 67. The electrostatic field applied at the transfer station is effec tive to attract the toner particles comprising the developed image 65a and causes them to adhere electrostatically to the surface of the copy material. The copy material supporting the toner developer particles in an imagewise pattern is carried along an endless belt configuration 85 so as to pass beneath a fixing unit, such as for example, a heat fuser 86, whereby the toner powder image on the sheet material is permanently fixed thereto. After fusing, the finished copy is discharged.

After passing the transfer station, the drum continues around and the working surface contacts the cleaning brush 88 which prepares the surface of the drum for a new xeroprinting cycle. Although the invention has been described in connection with corona charging, it is to be understood that this is exemplary only and the system may be employed with any other suitable technique. Other charging methods include friction charging and induction charging as described in U.S. Pats. 2,934,649 and 2,833,930 and roller charging as described in U.S. Pat. 2,934,650.

When used in the course of the present invention, the term injecting or imaging electrode should be understood to mean that it is an electrode which will preferably be capable of exchanging charge with the photosensitive particles of the imaging dispersion when the dispersion is exposed to light so as to allow for a net change in the charge polarity on the particle. By the term blocking electrode is meant one which is incapable of injecting electrons into or receiving electrons from the above mentioned photosensitive particles at more than a very slow rate when the particles come into contact with the surface of the electrode. Obviously, if all polarities in the system are reversed, the function of the electrodes will also be reversed.

It is preferred that the injecting electrode be composed of an optically transparent glass overcoated with conventional conductive material such as tin oxide, copper, copper iodide, gold or the like to obtain optimum results; however, other suitable materials including many semiconductive materials such as raw cellophane which are ordinarily not thought of as conductors but which are still capable of accepting injected charge carriers of the proper polarity under the influence of the applied field may be used in the course of this invention. The use of more conductive materials allows for cleaner charge separation and the charge leaving the particles upon exposure can move into the underlying surface and away from the particles in Which it originated. This also prevents possible charge buildup on the electrode which tends to diminish the interior electrode field. The blocking electrode, on the other hand, is selected so as to prevent or greatly retard the injection of electrons into the photosensitive particles when the particles reach the surface of this electrode. The blocking electrode drum or plate generally will consist of a material which is fairly high in electrical conductivity. Typical conductive materials are conductive rubber, and metal foils of steel, aluminum, copper and brass. Preferably, the core of the drum or base of the plate will have a high electrical conductivity in order to establish the required polarity differential. However, if a low conductivity material is used a separate electrical connection may be made to the back of the blocking layer of the electrode. Although a blocking electrode material need not necessarily be used on the surface of the electrode, the use of such a layer is preferred because of the markedly improved results which it is capable of producing. A detailed description of these improved results and the types of materials which may be employed as the blocking electrode materials is described in copending U.S. patent application Ser. No. 384,680, and now abandoned. It is preferred that the blocking layer when used be either an insulator or a semiconductor which will not allow for the passage of sufficient charge carriers under the influence of the applied field to discharge the particles finally bound to it thereby preventing particle oscillation in the system which results in enhanced image density and image resolution. Even if this blocking electrode will allow for the passage of some charge carriers through it to the photosensitive particles, it will still be considered to come within the class of preferred materials if it does not allow for the passage of sufiicient carrier to recharge the particle to the opposite polarity. Exemplary of the preferred blocking materials used is baryta paper which consists of paper coated with barium sulfate suspended in a gelatin solution and Tedlar, a polyvinyl fluoride commercially available from E. I. du Pont de Nemours. Although the invention has been described for the most part in connection with the use of baryta paper and T edlar as the blocking electrode material, any other suitable material, having a resistivity of about 10' ohms/cm. or greater may be employed. Typical materials in this resistivity range include cellulose acetate and polyethylene coated papers, cellophane, polystyrene, polytetrafluoroethylene, polyvinyl fiuoride, and polyethylene terephthalate. The baryta paper, Tedlar and other suitable materials used as the blocking layer may be Wetted on their back surface with tap Water or coated on the back surface with electrically conductive materials. A blocking electrode layer, when utilized, may be a separate replaceable layer which is either taped on the developing or blocking electrode or held by mechanical fasteners or any other device which is capable of releasably holding the layer on the electrode. In the alternative, the layer may be an integral part of the electrode itself, being either adhesively bonded, laminated, spray coated or otherwise applied to the surface of the roller. Other materials that may be used in the injecting electrode and blocking electrode, as Well as those electrophoretic particles which may be used as photosensitive pigments and the carrier liquids and operating conditions utilized with the system are to be found in the copending U.S. patent applications Ser. Nos. 384,737, now U.S. Pat. 3,384,565; 384,680; 384,681, and now abandoned; 468,935, now U.S. Pat. 3,474,020; and 473,607, and now abandoned, all of which are accordingly incorporated herein by reference.

Any suitable dielectric binder or insulating composition may be introduced into the photoelectrophoretic imaging system of the present invention such that it satisfies the requirements as herein defined. Typical insulating materials are Krylon, an acrylic ester resin commercially available from Krylon Incorporated; Viken, a vinyl plastic commercially available from the Chemical Rubber Company; polyvinyl acetate; polyvinyl chloride; Amoco resin 18, a polyalphamethyl styrene resin commercially available from Amoco Chemical Corporation; polyethylene waxes; halocarbon waxes, halogenated waxes commercially available from Halocarbon Products Corporation; polyethylene-ethylacrylate resin EA-2018, commercially available from Dow Chemical Company; Panarez resins, hydrocarbon resins commercially available from Amoco Chemical Corporation; Piccolastic A75, a polystyrene copolymer commercially available from the Pennsylvania Industrial Chemical Corporation; and Piccopale resins, unsaturated hydrocarbon resins commercially available from the Pennsylvania Industrial Chemical Corporation and mixtures thereof. When the procedure utilized is such that a spray or overcoating is applied it was found that the Krylon material produced optimum results and when the binder dielectric material was incorporated into the photoelectrophoretic suspension it was found that the Amoco resins furnished the most desirable results.

As mentioned above any suitable development means may be used to develop the xeroprinting image of the present invention such as cascade development more fully described in U.S. Pats. 2,618,551 and 2,618,552, powder cloud development more fully described in U.S. Pats. 2,725,305 and 2,918,910, magnetic brush development more fully described in U.S. Pats. 2,791,949 and 3,015,- 305, and liquid development as is more fully described in U.S. Pat. 3,084,043.

Any suitable toner developer may be used during the xeroprinting development stage of the process disclosed such as materials disclosed in U.S. Pats. 2,788,288, 3,079,342 and Reissue 25,136. Typical developer powders are styrene polymers, including substituted styrene such as the Piccolastic resins commercially available from the Pennsylvania Industrial Chemical Corp, phenol formaldehyde resins as well as other resins having similar properties. The developer powder or electroscopic marking particles may be applied directly to the latent image of the xeroprinting plate or admixed with a carrier, such as glass beads, as discussed above. The toner may be applied in the form of a mixture with magnetic particles, such as magnetic iron, to impart the necessary triboelectric charge to the developer powder particles. A developer particle is so chosen that it is attracted electrostatically to the charged image and/or repelled from the background area to the charged image and held thereon by electrostatic attraction or it may be chosen so as to electrostatically develop the uncharged areas by reversal development as discussed above.

Liquid developers may also be used when suitable in the course of the present invention. Typical developers are disclosed in US. Pats. 2,890,174 and 2,899,335. Generally, the developer comprises a liquid combination of mutually compatible ingredients which when brought into contact with an electrostatic latent image, will deposit upon the surface of the image in an imagewise configuration. In its simplest form, the composition may comprise a finely-divided opaque powder, a high resistance liquid and an ingredient to prevent agglomeration. Typical high resistance liquids include such organic dielectric liquids as carbon tetrachloride, kerosene, benzene, and trichloroethylene. The developer may comprise water alone or a mixture of liquids comprising a major proportion of water and a minor proportion of another solvent, such as an alcohol. The developer may be a polar liquid such as ethylene glycol, propylene glycol, or glycerol. Any of the finely divided opaque solid materials known in the art such as carbon black, talcum powder or other pigments may be used in the liquid developer. Other developer components or additives are vinyl resins, such as carboxy vinyl polymers, polyvinylpyrrolidones, methylvinylether maleic anhydride interpolymers, polyvinyl alcohols, cellulosics such as sodium carboxy-ethylcellulose, hydroxypropylmethyl cellulose, hydroxyethyl cellulose, methyl cellulose, cellulose derivatives such as esters and ethers thereof, alkali soluble proteins, casein, gelatin, and acrylate salts such as ammonium polyacrylate and sodium polyacrylate.

Any suitable aqueous base or oil based ink may be used in the process of the present invention either alone or in conjunction with the above liquid developer composition particularly when such developer is colorless. This includes both inks containing a water or oil soluble dye substance and the pigmented inks. Typical dye substances are Methylene Blue, commercially available from Eastman Kodak Company, Brilliant Yellow, commercially available from the Harlaco Chemical Co., potassium permanganate, ferric chloride and Methylene Violet, Rose Bengal and Quinoline Yellow, the latter three commercially available from Allied Chemical Company. Typical pigments are carbon black, graphite, lamp black, bone black, charcoal, titanium dioxide, white lead, zinc oxide, zinc sulfide, iron oxide, chromium oxide, lead chromate, zinc chromate, cadmium yellow, cadmium red, red lead, antimony dioxide, magnesium silicate, calcium carbonate, calcium silicate, phthalocyanines, benzidines, naphthols and toluidines. The pigmented inks are preferred inasmuch as the final print is longer lasting and possesses optimum optical density characteristics. Specifically preferred among the pigments is carbon black because it is more suitable for most printing operations.

Any suitable means may be used to transfer the developed image from the surface of the xeroprinting master to the transfer or copy sheet representing the final copy. A particularly useful and generally preferred method of carrying out the transfer operation comprises an electrostatic transfer technique wherein a transfer sheet is placed in contact with the image bearing surface or xeroprinting surface and an electric charge applied to the reverse side of the transfer sheet by, for example, an adjacent ion source such as a corona dischare electrode or other similar device placed in juxtaposition to the transfer member. Such an ion source may be similar to the source employed during the charging step of the xeroprinting process and is maintained at a high electrical potential with respect to the image bearing. Corona discharge occurs resulting in the deposition on the transfer sheet of ionized particles which serve to charge the member. The transfer member will be charged to a polarity opposite to that of the developed image and strong enough to overcome the potential initially applied to the surface of the xeroprinting master. Adhesive pickoff is another form of image transfer that may be used. The electrostatic transfer process is preferred in order to obtain maximum image transfer while retaining high image resolution. When liquid developers are employed a more generally preferred method of image transfer is that of applying contact pressure when the transfer member is brought into surface contact with the developed image.

The image formed on the surface of the transfer or copy sheet may be fixed to its support by any suitable means such as vapor fusing, treatment of the developed image with a regulated amount of heat or by a lamination process. It is preferred to use the heat fixing technique in conjunction with toner developed images inasmuch as it allows for a higher degree of control of the fixing phase of the process. When liquid developers have been used fixing is achieved by allowing for the evaporation of the relatively volatile carrier fluids utilized.

Any suitable material may be used as the transfer or copy sheet for the developed image during the xeroprinting process. The copy material may be insulating in nature or partially conductive. Typical materials are polyethylene, polyvinylchloride, polyvinylfiuoride, polypropylene, polyethylene terephthalate, and ordinary bond paper.

To further define the specifics of the present invention, the following examples are intended to illustrate and not limit the particulars of the present system. Parts and percentages are by weight unless otherwise indicated.

In the following examples, the imaging or injecting first electrode is made up of a NESA glass as described above and the surface of the glass is connected to ground. The development or blocking electrode consists of a hard conductive rubber core coated with a layer of waterproof baryta paper, unless otherwise indicated. A potential difference of 2500 volts is applied across the imaging suspension. The imaging suspension used in these examples consists of 7 parts by weight of photosensitive particles in Sohio Odorless Solvent 3440, a kerosene fraction commercially available from the Standard Oil of Ohio.

EXAMPLE I Utilizing a metal-free phthalocyanine pigment, Monolite Fast Blue GS, a photoelectrophoretic image is formed on the surface of the NESA glass upon exposure to a negative microfilm transparency. The image formed is a negative and similar in sense to the microfilm original. The imaged surface of the NESA glass is sprayed with a 6% solution of Krylon plastic consisting of polyvinyl methylmethacrylate dispersed in toluene so as to form a binder thickness of about 3 microns throughout the plate surface. The surface of the plate is then charged to a potential of about +500 volts with a corona discharge unit, exposed to light and toned using the cascade form of development, as described above. The toner comprises a polystyrene composition. The positive toned image is then transferred electrostatically to a paper transfer sheet and the xeroprinting cycle repeated.

EXAMPLE II The process of Example I is repeated with the introduction of a development electrode, such as is disclosed in US. Pat. 3,147,147, into the system. A photographic positive line image transparency is used as the input. The photoelectrophoretic image produced on the surface of the injecting electrode is now a replica of the positive line image. After overcoating with Krylon, charging to a potential of about +500 volts, exposing to a light source and cascaded developing the resulting latent image, the

1 l toner particles are transferred electrostatically to a paper transfer sheet. The resulting print is a negative reproduction of the original positive line image. The process is repeated thereby demonstrating the xeroprinting capabilities of the plate.

EXAMPLE III Utilizing a magenta pigment, Watchung Red B, 1-(4'- methyl--chloroazobenzene-2'-sulfonic acid)-2-hydroxy 3-naphthoic acid, C.I. No. 15,865, commercially available from E. I. du Pont de Nemours & Co., a photoelectrophoretic image is formed on the surface of the NESA glass upon exposure to a negative microfilm transparency. The imaging suspension contains about 5% by weight of Amoco resin 18 at a thickness of about 4 The imaged surface of the plate is then charged to a potential of about +500 volts with a corona discharge unit, exposed to light and developed with a liquid developer consisting of about carbon black, 10% silica aerogel and 80% kerosene liquid vehicle. The developed image is then contacted under pressure with the surface of a paper transfer sheet and the liquid released to the surface of the transfer sheet in an imagewise pattern. Upon evaporation of the volatile carrier a positive image is obtained on the paper sheet. The xeroprinting cycle is repeated thereby illustrating the duplicating capabilities of the prepared master.

EXAMPLE IV The process of Example III is repeated except that a cellophane sheet is placed on the surface of the NESA electrode and the photoelectrophoretic image formed thereon. The cellophane sheet is then used in conjunction with the remaining steps of the process as a xeroprinting master.

EXAMPLE V The process of Example I is repeated up to and including the step of the formation of the image on the NESA drum. The photoelectrophoretic image is then transferred to the surface of a conductive paper sheet according to the process disclosed in U.S. patent application Ser. No. 542,- 050, filed Apr. 12, 1966, and the sheet sprayed with a 6% solution of Krylon as in Example I. The surface of the image sheet is then charged to a potential of about +500 volts with a corona discharge unit, exposed to light and toned using the cascade form of development and a toner composition comprising polystyrene as in Example I. The toned image is then transferred electrostatically to a paper transfer sheet and the xeroprinting cycle of charging, exposing, and developing repeated.

EXAMPLE VI The process of Example I is repeated except that a Trimix prepared by dispersing equal parts of a cyan pigment, Monolite Fast Blue GS, a mixture of the alpha and beta forms of metal-free phthalocyanine, commercially available from Arnold Hoffman Co.; a magenta pigment, Watchung Red B, 1-(4-methyl-5'-chloroazobenzene- 2-sulfonic acid)-2-hydroxy-3-naphthoic acid, C.I. No. 15,865, available commercially from E. I. du Pont de Nemours & Co., Inc.: and a yellow pigment, Algol Yellow GC, 1,2,5,6-di-(C,C'-diphenyl)thiazole anthraquinone, C.I. No. 67,300, commercially available from General Dyestuifs, in the above mentioned Sohio Odorless Solvent 3440 is substituted for the Uni-pigment mix. The remainder of the process is diuplicated. Similar results were obtained.

Although the present examples were specific in terms of conditions and materials used, any of the above listed typical materials may be substituted when suitable in the above examples with similar results. In addition to the steps used to carry out the process of the present invention, other steps or modifications may be used, if desirable. For example, the preparation and use of the xeroprinting master may be combined into one continuous operation and configuration. In addition, other materials may be incorporated in the electrophoretic imaging suspension, injecting electrode, blocking electrode or xeroprinting system, which will enhance, synergize or otherwise desirably afiect the properties of the system for their present use. For example, the imaging suspension may contain sensitizers for the photosensitive particles which are dissolved or suspended in the carrier liquid.

Anyone skilled in the art will have other modifications occur to him based on the teaching of the present invention. These modifications are intended to be encompassed within the scope of this invention.

What is claimed is:

1. A method of preparing multiple copies from a xeroprinting master which comprises:

(a) subjecting a layer of a photoelectrophoretic imaging suspension to an applied electric field between at least two electrodes, at least one of which is partially transparent, said suspension comprising a plurality of photoelectrophoretic imaging particles in an insulating carrier liquid,

(b) selectively exposing said suspension to electromagnetic radiation through said transparent electrode in the presence of said electric field, thereby forming complementary images on the surfaces of said electrodes,

(c) transferring one of said images to the surface of a conductive substrate,

(d) uniformly applying to the surface of said image lbearing substrate an organic insulating hinder composition such that the binder thickness both Within the image formed and the non-image areas ranges from about 1 to about 20 microns,

(e) applying a uniform charge to the surface of said image bearing conductive substrate in the presence of electromagnetic radiation thereby forming an electrostatic residual charge pattern corresponding to the non-image areas,

(f) developing said residual charge pattern with a developer composition,

(g) transferring said developer composition from the residual charge pattern to the surface of a copy sheet, and

(h) repeating steps e through g at least one time.

2. A method of making multiple copies from a xeroprinting master which comprises:

(a) subjecting a layer of a photoelectrophoretic imaging suspension to an applied electric field between at least two electrodes, at least one of which is partially transparent, said suspension comprising a plurality of photoelectrophoretic imaging particles in an insulating carrier liquid,

(b) selectively exposing said suspension to electromagnetic radiation through said transparent electrode in the presence of said electric field, thereby forming complementary images on the surfaces of said electrodes,

(c) separating said electrodes,

(d) uniformly applying to the surface of one of said image bearing electrodes an organic insulating binder composition such that the binder both within the image areas formed and in the non-image areas ranges in thickness from about 1 to about 20 microns,

(e) applying a uniform charge to the surface of said image-bearing electrode in the presence of electromagnetic radiation to produce an electrostatic residual charge pattern corresponding to said nonimage areas,

(f) developing said residual charge pattern with a developer composition,

(g) transferring said developer composition corresponding to said residual image pattern to the surface of a copysheet, and

References Cited UNITED STATES PATENTS Carlson 117-17.5X Oster 204-180 Johnson 204-181 Robinson 961.4 Matkan 117-371X Yeh 204181X Tulagin et a1. 204-181 Bartfair 961.5X

Lennon 204--181X Mihajlov 20'4181X Copley 96-1.4

CHARLES E. VAN HORN, Primary Examiner US. Cl. X.R. 

